1. Field
Embodiments of the present invention relate to a display device and a method for driving the same.
2. Description of the Related Art
Various types of flat panel displays (FPDs) that have reduced weight and volume compared to a cathode ray tube (CRT) are currently being developed. The FPDs include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), organic light emitting diode (OLED) displays, and the like.
Among the FPDs, the OLED display displays images using organic light emitting diodes (OLEDs) that generate light by recombining electrons and holes, and it is drawing attention owing to aspect such as short response time, low power consumption, high luminous efficiency, improved luminance and viewing angle.
The OLED display can be generally classified into two types according to the driving method of the OLED: a passive-matrix OLED (PMOLED) and an active-matrix OLED (AMOLED).
Of the two types, the active-matrix OLED, in which unit pixels are selectively lit in terms of resolution, contrast, and operation speed, is primarily used.
One pixel of the active-matrix OLED includes an OLED, a first transistor for controlling an amount of current applied to the OLED, and a switching transistor for transmitting a data signal to the first transistor to control an amount of light emitted by the OLED.
Recently, research on a compensation circuit has been carried out to compensate for a threshold voltage variation of the first transistor included in the pixel of the active-matrix OLED. However, in the case where the compensation circuit is used to display a target luminance, the response time varies depending on increases or decreases of data voltage due to hysteresis such that it is difficult to correctly display gray levels. For example, the response time may be delayed when the OLED display is driven to display luminance from black to white, and this problem may cause sticking when a text is scrolled on a screen.
In order to decrease (e.g., improve) the response time, a driving method of applying on-bias voltage to the first transistor before an initialization period has been suggested. However, a characteristic curve of the first transistor changes when the on-bias voltage is applied, thereby causing smear on the screen when the gray levels are displayed.
Therefore, a pixel circuit is desired to compensate for the threshold voltage variation of the first transistor included in the pixel, and mitigate (e.g., solve) the change of the response time due to the hysteresis and reduce the smear resulting from the on-bias voltage application.